There is a scene in Charlie And The Chocolate Factory in which one of the children, Augustus Gloop, is so greedily scooping up chocolate from the chocolate river that he falls in and gets sucked into the pipes of the huge chocolate-making machine. I am standing in a barn in the south of France, feeling as if I'm about to do an Augustus Gloop. In front of me are five wicker baskets, each spilling over with jasmine destined for the Chanel factory in Paris and, eventually, to be turned into Chanel No 5, one of the world's most successful perfumes. As I kneel to touch the delicate white flowers, it's all I can do to stop myself falling in. The air is so heavy with their scent, you can taste it in the back of your throat - it's intoxicating. The barn itself is as rustic as it gets: all rickety furniture, faded white walls and wooden shutters. Outside, you can smell jasmine in the breeze, and there's the added romance of the late summer light making the endless fields of the stuff look like the perfect bridal bouquet. This place could not be further from the harsh lighting of the beauty halls across the world, where a bottle of Chanel No 5 is said to sell every 30 seconds.

I'm no perfumer, but I hadn't expected anything so lo-tech. The jasmine is picked by hand (to give an idea of the scale of the operation, 1kg of jasmine amounts to about 8,000 flowers, and 700kg are needed to make one litre of absolute, the pure oil derived from the pressed petals), and then put in the wicker baskets and loaded on to a van for the short journey to the other end of the farm. It is pressed overnight and the essential oils extracted. The process hasn't changed since 1921, when Gabrielle Chanel (Coco was a nickname given by her father) paid the farm her first visit. There are no computers, no whizz-bang technology; in fact, the most hi-tech thing is the van, and that, too, has a distinctly old-school feel to it.

Joseph Mul, who owns the farm with his brother Marius, is as close to a caricature of a French farmer as you could get: his complexion is ruddy, his eyes twinkly and his Gallic charm on full throttle. The farm in Grasse, about a half-hour's drive from Nice, has been in his family for five generations - grandmother Mul was around in 1921 when Chanel and perfumer Ernest Beaux collaborated to create No 5. Chanel is said to have asked Beaux to design "a fragrance for women that smells like a woman". The result was No 5, with its distinctive notes of ylang-ylang, jasmine and May rose. It got its name because it was the fifth prototype Beaux presented to Chanel (it was also her lucky number: collections were always shown on the fifth of the month).

The fashion at the time was for fragrances that were as over the top as the baroque bottles in which they were sold. Perfumes had names such as Nuit de Chine, and you could always relate them to a particular scent: the smell of rose, vanilla or spice, say. With its heady florals, No 5 was revolutionary, as was its stark bottle. Like the process by which the jasmine is collected, neither the smell nor the bottle shape of No 5 has changed since its inception. If you have ever bought or been given a bottle of Chanel No 5, the jasmine (and the May rose, for that matter) will have come from this farm.

For the past 25 years, the person responsible for ensuring that No 5 stays the same is Jacques Polges, the head "nose" at Chanel. Polges' nose is up there with David Beckham's right foot and Jennifer Lopez's behind - if it hasn't been insured for vast amounts of money, then it should be.

If you own a bottle of Chanel perfume, chances are it, or some element of it, has been sniffed by Polges. At the start of the 20th century, perfume houses had a "nose" as a matter of course. Now, with most of the independent perfumers having been bought up by multinationals, they are a dying breed. Polges, the third generation of nose at Chanel, likens his role to that of a chef, and views the disappearance of his art with sadness. "What would you think of a restaurant that brought the food in from somewhere else?" he says of those who get others to design their fragrances for them.

"My role in the lab is threefold - first, the creation of every scent; second, the selection of all raw materials that participate in the concentrate of all the perfumes, even those created by predecessors"; and the last part is about control. "Nothing," Polges says, "goes into the plant as far as perfumes are concerned without my OK, and nothing goes out of the plant without my approval." He spends most mornings smelling bits of paper (this is when the nose is at its "freshest", apparently) and the afternoons working on his concoctions in the lab. He also spends time smelling the competition, though when asked to name his favourite scent, he is endearingly proud of his own creations. "My favourite women's perfume is Coco Mademoiselle, because it is very successful among young people, and my favourite men's fragrance is Egoïste - in the men's market, it is the most different."